lOJ On the Cause of Chemical Propmtions. [Feb. 



with sulphuric acid : therefore the 9-877- of chioniate of lead con-- 

 tain 6/3 of oxide of lead ; so that this chioniate is composed of 



Chromic acid 31-7GI TOO 



Oxide of kad 68-239 213-841 



100000 



' Now 213-S41 of oxide of lead contain J 5-29 of oxygen. Hence 

 chromic acid must coniaia 2, 3, or 4 tiases that quantity of oxygen. 

 Ten parts of native cln-omate'of lead (in picked crystals) treated 

 %vith a mixture of alcohol and muriatic acid, were almost imme- 

 diately decorapobed, with the disengagement of heat, and the pro- 

 duction of ether. The muriate of lead remained undissolved, while 

 the muriate of chromium dissolved in the spirituous liquor. The 

 liquor being evaporated nearly to dryness to get rid of the excess of 

 acid, 1 mixed the residue with alcohol to dissolve the muriate of 

 chromium. The muriate of lead, being well washed with alcohol, 

 was dissolved in water, and left undissolved 0-1 of foreign matter. 

 I evaporated the solution of muriate of lead in a platinum crucible, 

 exactly weighed, and I dried the muriate on a sand-bath at a high 

 temperature : 1 obtained 8'4S.'i parts of muriate of lead. The 

 solution of muriate of chromium precipitated by anmionia gave 

 green oxide of chromium, which, when heated to redness, weighed 

 2-388. The residup.l ammoniacLil liquid being evaporated to dry- 

 ness and calcined, left 0-013 of green oxide of chromium. Now 

 as 99 parts of chrctnate of lead produced 84-35 of muriate of lead, 

 which contains 60-3376 per cent, of oxide of lead {Ann. de CJiim, 

 Aug. 1811, p. 1S6), it follows that the chromate ought to be 

 composed of 



Oxide of lead 68-50 



Green oxide of chromium 24-14 



Loss =; oxygen of the acid 7'>^6 



100-00 



This analysis does not differ from the preceding synthesis but i 

 per oeiit., and may therefore be considered as pretty exact. It 

 follows ih It 31*5 of chromic acid are composed of 24-14 of green 

 oxide and 7'''^^ of oxygen : but the 68-5 of oxide of lead contain 

 4-8997 of oxygen, which is not a submultiple of T'^d by a whole 

 number: but 7*36 is exactly \\ times the oxygen in the oxide of 

 lead; for 4-8997 x 1} = 73465. Hence we see that the acid 

 had lost 14 times asniiuch oxygen as the base contains. 



B. Chromate of- Borytes. — This fact required to be verified by 

 another experiment. I therefbre treated 10 parts of chromate of 

 barytes previously heated to redness with a mixture of muriatic acid 

 iind alcoiiol. J then separated the barytes by means of sulphuric 

 acid. I obtained 9-1233 parts of sulphate of barytes; therefore 

 chroojate of- barytes is composed of 



